The long range goal of these studies is to understand how genomic repair and recovery systems alter mutagenesis and lethality in somatic mammalian cells. These studies are important because it appears that a great deal of human cancer and probably also genetic disease are caused by mutations. The production of mutations, however, seems not to be a passive process that results automatically when the genome is damaged but instead depends on the activity of repair systems which can, in ways not yet understood, actually cause mutagenesis. Such systems are well known in bacteria, where they are termed error-prone or SOS repair, since they are often inducible by mutagens which damage the genome. In mutant bacteria in which such repair systems are genetically absent, mutation cannot be induced. The existence of these kinds of repair in mammalian cells is disputed. We have produced a mutant, termed UV-1, from Chinese hamster ovary cells that has increased susceptibility to killing by mutagens, hypomutability, and defective post replication recovery (PRR). We have proposed that UV-1 is defective in an error-prone repair process associated with PRR. We have converted UV-1 back to normal resistance and PRR by DNA mediated gene transfer of human DNA into UV-1. This now should allow us to isolate and characterize the human DNA responsible for restitution of the normal phenotype(s). Specifically, we intend to define exactly which properties of UV-1 may be corrected by transformation with human DNA; to clone the transforming DNA into an appropriate vector; to map the gene(s) to specific human chromosomes; to examine possible relationships of these genes to those deficient in human diseases such as xeroderma pigmentosum, ataxia telangiectasia, Cockayne's Syndrome and other diseases which are associated with defective repair; and to begin to characterize this DNA by restriction mapping, isolation of unique sequences, preparation of cDNA clones, and identification of possible messenger sequences. Finally we will carry out studies of its expression, particularly with regard to inducibility.